1. Field of the Invention
This invention relates to coal gasification fluid beds used in combination with stand pipes or tubes which operate substantially to isolate the fluid of the fluid bed side from that of the tube side, wherein particles are transferred from the fluid bed to the tube side by means of an ejector nozzle utilizing the Venturi Principle.
2. Description of the Prior Art
The technology relating to the agitation of a column of particulate solids by means of introducing gases or other fluids to develop a fluid bed zone is a well developed art. The dynamic conditions required to establish a fluidized state of particulate matter are well defined in current literature and need not be further developed herein.
Generally, the particulate matter is retained in a tank or shell with the column of particles being partially supported by a base or a distributor plate. Customarily, the distributor plate contains a plurality inlets or ducts through which the gas or other fluid is forced to activate a fluidized state. The random motion of the particles caused by the circulating fluid permits rapid heat transfer and difusion of reactant gases throughout the fluid bed.
Because of the improved heat transfer and difusion of reactants, fluid bed systems are particularly useful as reaction sites in systems where the primary interaction occurs between particles and a fluid phase reactant, such as coal gasification for production of fuel gases.
With the increased interest in coal gasification, numerous fluid bed systems have been developed for reacting coal particles with steam. A typical reaction sequence for this process is as follows: EQU (1) C + H.sub.2 O.sub.(steam) .fwdarw. H.sub.2 + CO EQU (2) c + o.sub.2 (heat) CO.sub.2 + heat EQU (3) CO + H.sub.2 O .fwdarw. H.sub.2 + CO.sub.2 EQU (4) 3h.sub.2 + co .fwdarw. ch.sub.4(gas) + H.sub.2 O
reactions (1) and (2) customarily occur in a single chamber, with reaction (2) furnishings the heat for reaction (1). The final reaction is (4) which yields the desired methane gas (CH.sub.4). Because of the requirement for a 3:1 ratio of H.sub.2 to CO in reaction (4) an additional source of H.sub.2 is required. Reaction (3), sometimes referred to as the water-shift reaction, provides the additional H.sub.2 to reach the necessary stoichiometric concentrations of H.sub.2 and CO.
The water-shift reaction is required when air or O.sub.2 is fed into the coal reaction zone with the steam, since reactions (1) and (2) produce relatively large amounts of CO and CO.sub.2 with a corresponding lesser volume of H.sub.2. When air is used for the combustion reaction (2), the additional constituent of N.sub.2 further reduces the relative percent of usable raw gas. A preferred system would isolate reactions (1), (3) and (4) from (2) such that the H.sub.2 produced in (1) would further react with the CO concurrently produced, leading to an isolated reaction sequence as follows: EQU (1) 2C + 2H.sub.2 O (steam) .fwdarw. 2H.sub.2 + 2CO EQU (3) 2co + 2h.sub.2 o (steam) .fwdarw. 2H.sub.2 + 2CO.sub.2 EQU (4) 3h.sub.2 + co .fwdarw. ch.sub.4 + h.sub.2 o
because isolation has not heretofore been achieved on an economical basis, however, the fuel gas from current coal gasification processes requires additional steps in reaching the primary CH.sub.4 product, and yields a combination of gases including CO.sub.2 and N.sub.2, possessing a lower BTU rating per volume of gas.
In addition to problems arising from combining the combustion reaction with the steam reaction, current reaction systems require means for withdrawing ash and other unconsumed miner by-products from the reaction shell, disposing of such materials as waste. Since this disposal process usually requires mechanical power without adding new energy, the net energy produced by the system is further decreased. A preferred system would involve minimum consumption of carbonaceous materials and minimal power requirements for disposal of remaining by-products, as well as minimal amount of thermal loss by any other means.
These specific illustrations are merely representative of a broad field of art that would generically be described as fluid bed reaction systems where separate reaction zones may be utilized to improve overall efficiency in yielding the desired product. Such systems will frequently involve requirements for heat transfer from a first reaction site to a second reaction site and would have to have communication therebetween which is compatable with the existence of a fluid bed in at least one of the sites.